The invention is directed to an optical switch and more particularly to an optical switch having a converging optical element.
Optical switches for switching light signals between different optical fibers are known. A known optical switch 100 is shown in FIGS. 1A, 1B, 1C and 1D. The optical switch 100 is composed of input collimator array 110 for receiving multiple light beams, each representing an optical signal, via associated optical fibers 50. For clarity, only one optical fiber is shown in FIGS. 1A, 1B and 1D. A light beam is output from input collimator array 110 and directed onto a first micromirror that forms part of input micromirror array 120. The first micromirror can be rotated about at least one axis to direct the light to a second micromirror the forms part of output micromirror array 121. The second micromirror can be rotated about at least one axis to direct the light beam received from the first micromirror into the collimator corresponding to the second micromirror. The collimator is part of the output collimator array 111. Micromirror arrays 120 and 121 each incorporate micromirrors 25 (FIG. 1C).
In the optical switch 100, the input collimator array 110 must be very accurately aligned with respect to the input micromirror array 120 to make the light beam output by each collimator impinge on the center of the micromirror associated with that collimator. To achieve this alignment throughout the input collimator array, the collimators must be aligned so that they output light beams that are accurately parallel to one another. Such accuracy is difficult and expensive to achieve in production. Additionally, the input collimator array must incorporate custom collimators that each generate an output light beam that converges at the input micromirror array. This is less convenient and more expensive than using a standard collimator that generates parallel output light beam.
Similar considerations apply to the output collimator array 111, which must be accurately aligned with the output micromirror array 121 to ensure that the optical signal reflected by a particular output micromirror is properly coupled into its associated collimator of the output collimator array. Moreover, the optical beam propagates directly from the input micromirror array to the output micromirror array. As noted above, the collimators of the input collimator array should be configured to ensure that the light beam has the correct waist and curvature at the input micromirror array. Otherwise, the free space propagation of the light beam from the input micromirror array to the output micromirror array results in the light beam expanding to be much larger than the micromirrors of the output micromirror array.
A second example of a known optical switch is shown in FIG. 1D. In this, a fixed mirror 125 is interposed between an input micromirror array 120 and an output micromirror array 121 to redirect the light beam from input micromirror array 120 onto output micromirror array 121. Folding the optical path between the input micromirror array and the output micromirror array in this manner reduces the dimensions of the optical switch. However, as the fixed mirror 125 is flat, expansion or contraction of the beam diameter between the input and output micromirror arrays 120 and 121, respectively, occurs as if the mirror were not present. As before, the collimators of the input collimator should be custom devices configured to ensure the proper waist w0 and curvature of the optical beam at the input micromirror array 120.
In the optical switches just described, the beam size at the output micromirror array limits how small the micromirrors may be. Large micromirrors increase the physical size of the optical switch and require more energy to switch them quickly. Moreover, a beam size larger than the micromirrors attenuates the optical signal, and can additionally result in crosstalk between the different optical signals that pass through the optical switch. Also, as described above, the alignment between the micromirror arrays and their respective collimators is critical. Finally, in the optical switches just described, approximately half of the angular range of those of the micromirrors located at and near the edges of the array is wasted. This means that, if all the micromirrors are identical as is usually desirable, fabrication of the micromirrors is more difficult than it need be because of the need to provide them with an increased angular range.
Thus, what is needed is an optical switch in which the beam size of the light beams that pass through the optical switch is small at the micromirror arrays, in which the alignment between the micromirror arrays and their respective collimators is less critical, in which the collimators do not have to output light beams that are accurately parallel, in which standard collimators that generate parallel beams of light can be used and in which micromirrors having an angular range corresponding to that of the micromirrors near the center of the array can be used throughout.
The invention provides an optical switch that comprises an input collimator, an output collimator, an input mirror, an output mirror and a converging optical element. The input collimator receives, collimates and outputs an input light beam. The input mirror is arranged to receive the light beam from the input collimator. The output mirror is arranged to receive the light beam reflected by the input mirror and reflects the light beam into the output collimator. The converging optical element is located to receive the light beam reflected by the input mirror and reflects the light beam onto the output mirror.
The converging optical element is located relative to the input mirror and the output mirror such that the waist of the light beam at the output mirror is similar in size to that at the input mirror.
An imaging element may be located between either or both of the input collimator and the output collimator and a respective one of the input mirror and the output mirror. The imaging element makes alignment between the collimators and their respective mirrors less critical, allows collimator forming part of an array to output respective light beams at different angles and allows the full range of angular movement of the mirror to be used.
The invention also provides an optical switch that comprises an input collimator, an output collimator, an input mirror, an output mirror and an imaging element. The input collimator receives, collimates and outputs an input light beam. The input mirror is arranged to receive the light beam from the input collimator. The output mirror is arranged to receive the light beam reflected by the input mirror and reflects the light beam into the output collimator. The imaging element images at least one of the input collimator and the output collimator on a respective one of the input mirror and the output mirror. The advantages conferred by the imaging element are described above.
The invention additionally provides a first method for switching an optical signal. In this, an optical switch including an input mirror and an output mirror is provided. The light beam is received, and is directed towards the input mirror. The orientation of the input mirror is adjusted to direct the light beam onto the output mirror. The light beam is converged after reflection by the input mirror and prior to reflection by the output mirror. The orientation of the output mirror is also adjusted.
Finally, the invention provides a second method for switching an optical signal. In this, an optical switch including an input collimator, an input mirror, an output mirror and an output collimator is provided. At least one of the input collimator and the output collimator is imaged onto a respective one of the input mirror and the output mirror. The light beam is received at the input collimator. The orientation of the input mirror is adjusted to direct the light beam onto the output mirror. The orientation of the output mirror is also adjusted.
Other apparatus, methods, features, and advantages of the invention will be or become apparent to one of ordinary skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional apparatus, methods, features and advantages disclosed in this description be within the scope of the invention, and be protected by the accompanying claims.